Aviation safety investigations & reports

Piper Aircraft Corp PA-31-350, VH-UBC

Summary

History of the flight

The Piper Aircraft Corporation PA-31-350 Navajo Chieftain,
registered VH-UBC, departed Albury on a charter flight with a pilot
and six passengers on board. About 5 minutes into the flight, as
the aircraft climbed through approximately 5,000 ft, the pilot
reported that the right fuel flow light illuminated. The pilot
moved the right engine mixture control lever to full rich and
advised the Albury Tower controller that he was returning to
Albury. A short time later, the right engine started surging. The
pilot reported that he changed the right fuel selector from the
inboard to the outboard tank selection, although he was aware that
there was only a small quantity of fuel in that tank. The engine
continued to surge and he reselected the inboard tank. The pilot
reported that he did not shut down the engine and feather the
propeller because he thought the engine was producing some
power.

The pilot reported that approximately a minute after the onset
of the right engine problem, the left fuel flow light illuminated
and the left engine also started surging. He advised the controller
that he was diverting to Holbrook. The pilot found a break in the
clouds and descended the aircraft, maintaining visual contact with
the ground. On levelling out after the descent through cloud, he
reported that the engines operated smoothly, but at reduced power.
He reported that he maintained blue line speed for a short time,
before power reduced to a level which would not allow altitude to
be maintained. During the descent, the pilot opened the crossfeed
valve and checked that all fuel pumps were on, mixture controls
were rich and the inboard tanks selected. Unable to restore power,
the pilot decided to make an emergency landing in an open field
below the aircraft. Before landing, the pilot extended the flaps
and the landing gear and instructed the passengers to prepare for
an emergency landing.

The aircraft contacted the ground with its right wingtip and
slewed for approximately 93 metres while rotating almost 180
degrees to the right. The aircraft was substantially damaged, but
there was no fire. Neither the pilot nor the passengers sustained
any injuries. The pilot reported that before exiting the aircraft
he switched off the fuel pumps, magnetos and master switches.

Weather

The weather at Albury and the surrounding area was overcast with
low cloud and fog patches. Rain and isolated thunderstorms were
forecast for the area. Moderate icing was forecast above 10,000
feet.

Pilot qualification

The pilot held a Commercial Pilot Licence (Aeroplane) with a
Multi-engine Command Instrument Rating and was appropriately
endorsed on the aircraft type. He held a valid Class 1 medical. On
4 August 2003 he satisfactorily completed a type proficiency check
on the Chieftain aircraft. Although not a training and checking
requirement for charter flights, the operator additionally
stipulated this check for its pilots.

Aircraft

The aircraft was owned by a locally based company that used it
to transport its employees between numerous production facilities
and was operated by an Albury based charter and training operator
on their behalf.

The aircraft was maintained in accordance with the maintenance
requirements applicable at that time and had a valid Maintenance
Release. It had flown approximately 50 hours since the last
maintenance release (periodic) inspection. There were no
outstanding maintenance issues at the time of the accident.

Fuel status

The aircraft had flown during the previous day, returning to
Albury late that afternoon. The pilot who flew the aircraft that
day reported that the aircraft and its systems operated normally.
He refuelled the aircraft for the next day's flying, filling only
the inboard tanks. No fuel was added to the outboard tanks and the
pilot estimated that about 25 to 35 litres remained in each
outboard tank.

The rostered pilot reported that, on the morning of the
occurrence, he carried out a preflight check during which he
visually inspected the fuel tank contents. The pilot reported that
he found both inboard tanks full, but could not see any fuel in the
outboard tanks. In accordance with the operator's practice, the
pilot started and warmed the engines so that the flight could
proceed without delay when the passengers arrived.

The `Before starting engine' and `Before take off' checklist
procedures required the pilot to check that the fuel selector
valves were selected to INBOARD tanks. Both the manufacturer's and
the operator's `Before taxiing' checklist procedures then required
the pilot to check the fuel selector at each detented position. The
operator reported that pilots were encouraged to check the
operation of the fuel selector valves in all detented positions
during the engine warm up run. The pilot reported that in order to
conserve the fuel in the inboard tanks for the trip, he preferred
to warm the engines using the fuel from the outboard tanks.

The departure had been delayed due to fog at the destination.
The flight commenced approximately two hours later than planned,
when the fog cleared. The pilot reported that he carried out
another engine warm up with the passengers aboard and had checked
the INBOARD tanks selection before takeoff.

Fuel system

The aircraft fuel system consisted of four fuel cells, two in
each wing, and had a total capacity of 734 litres, of which 690
litres were useable. It was also fitted with two long-range nacelle
tanks that were not used on this flight. The inboard tanks each had
a capacity of 212 litres and each of the outboard tanks 155 litres.
The tanks were a bladder type and were located between the main and
the rear wing spars. The filler caps were located at the outboard
end of each tank. The slenderness of the tanks and the wing
dihedral resulted in the fuel accumulating at the inboard end of
each tank. That meant that unless the tank was full, or nearly
full, it was not possible to assess the quantity of fuel remaining
in the tank by visual inspection or by dipping through the filler
cap opening.

The left and the right wing fuel systems were independent. Two
fuel selector valves, one for each wing's fuel system, allowed the
pilot to select either OUTBOARD, OFF or INBOARD positions. When a
tank was selected, the fuel was fed to the respective engine
system. A crossfeed line with a crossfeed valve was the only
interconnection between the two wing fuel systems. The crossfeed
valve is normally closed.

Wreckage Examination and Component Testing

The aircraft sustained substantial damage during the emergency
landing. The right wing was damaged, the landing gear was torn off
and both propellers damaged. Damage to the blades of both
propellers was almost identical and was consistent with them
rotating at impact. Calculations based on an aircraft speed of
about 110 kts, as reported by the pilot, and propeller blade slash
marks at the initial point of impact, indicated that both
propellers were rotating at approximately 1,830 RPM at impact.

When visually inspected through the filler caps shortly after
the accident, both inboard tanks were full, but no fuel could be
seen in the outboard tanks. The investigation determined that there
were 210 to 211 litres of fuel in each inboard tank. The right
outboard tank contained approximately 25 litres and the left
outboard tank approximately 1 litre of fuel.

Detailed examination of the tanks and the fuel system found no
evidence of flow restriction or the presence of any foreign
material inside the system. Fuel samples taken from the aircraft
were tested and found to comply with the respective fuel
specification. The fuel was of the correct type and grade for the
aircraft.

Both engines were removed from the aircraft. When tested, they
operated normally in accordance with the manufacturer's test
schedule. There was no evidence of any defect that would have
accounted for the reported malfunction.

The fuel system and its components were tested in situ, and
found to operate normally. The selector valves and the pumps were
removed and tested. Operation of all but the left high-pressure
fuel pump was normal.

The left high-pressure fuel pump failed to deliver the required
pressure and fuel flow and was found to leak at the rate of about
1/4 litre per minute. The test facility specialist reported that
the possibility of the fault resulting from damage during the
accident could not be excluded.

There was no evidence of any other abnormality of the individual
fuel system components and controls.

Fuel consumption

Calculated fuel consumption, based on the manufacturer's Take
Off and Climb performance charts, determined that from the time the
aircraft commenced take-off to its emergency landing, approximately
32 litres of fuel would have been consumed. In addition 12 litres
of fuel was estimated to have been used during the engine warm ups
and taxiing.

Analysis

The descriptions of the loss of engine power and the subsequent
engine surging were consistent with fuel starvation, a situation
where the fuel to the engine is interrupted, although there is
adequate fuel on board the aircraft.

Although the left high-pressure fuel pump failed to deliver the
required pressure and fuel flow and was found leaking during
subsequent testing, it would have had little effect on the
development of the occurrence and its defect may have occurred
during the accident sequence.

The pilot reported that he had selected inboard tanks for the
flight. The investigation was unable to reconcile the pilot's
reported recollection of inboard tank selection and the evidence of
the remaining fuel quantities in the inboard tanks.

Safety Action

Local safety action

Aircraft operator

As a result of the contractor's requirements, the operator
reported that future flights for the contractor would be operated
by two pilots.

Australian Transport Safety Bureau

Fuel exhaustion and starvation accidents accounted for over 6
per cent of all accidents between 1991 and 2000 and the rate
remains relatively constant.

In December 2002 the ATSB published a research paper titled
`Australian Aviation Accidents Involving Fuel Exhaustion and
Starvation'. It is available on the ATSB's website www.atsb.gov.au,
or from the Bureau on request.